The present invention relates to a pneumatic tire, more particularly to an improved tread structure being capable of improving ride comfort as well as steering stability and high-speed durability.
Pneumatic tires whose tread rubber is composed of a radially outer layer of softer rubber and a radially inner layer of harder rubber are widely used. The main object of this double-layered structure is to improve the ground contact by the softer rubber and improve the steering stability and high-speed durability by the harder rubber.
In such a double-layered structure, as the hardness of the inner rubber layer is increased, the steering stability and high-speed durability can be improved. But, the ride comfort deteriorates.
It is therefore, an object of the present invention to provide a pneumatic tire, in which ride comfort can be improved as well as steering stability and high-speed durability.
According to the present invention, a pneumatic tire comprises a carcass extending between bead portions through a tread portion and sidewall portions, a belt disposed radially outside the carcass in the tread portion, and a tread rubber disposed radially outside the belt, wherein
the tread rubber comprises an axially inner base rubber layer, a pair of axially outer base rubber layers, and a radially outer tread rubber layer, the axially inner base rubber layer disposed on the radially outside of the belt and centered in the tread width, the axially outer base rubber layers disposed one on each side of the axially inner base rubber layer, on the radially outside of the belt, the radially outer tread rubber layer disposed over the radially outside of the axially inner and outer base rubber layers,
the hardness HC of the radially outer tread rubber layer is in a range of from 60 to 80 degrees,
the hardness HB1 of the axially inner base rubber layer is in a range of from 50 to 65 degrees,
the hardness HB2 of the axially outer base rubber layers is in a range of from 75 to 95 degrees, and
they have a relationship of HB1 less than HC less than HB2.
Here, the hardness of rubber is defined as measured with a type-A durometer according to Japanese Industrial Standard K6253.
An embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings.
FIG. 1 is a cross sectional view of a tire according to the present invention.
In FIG. 1, pneumatic tire 1 according to the present invention comprises a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4 each with a bead core 5 therein, and it is provided with a carcass 6 extending between the bead portions 4, and a tread reinforcing belt disposed radially outwardly the carcass 6 in the tread portion 2. The aspect ratio of the tire is less than 60%.
In this embodiment, the pneumatic tire is a high-performance radial tire of size 225/50R16 for passenger cars.